The present invention relates generally to electronic data storage and, more particularly, to methods for long-term storage of data in volatile memory.
Computer systems, regardless of manufacturer or size, typically employ at least the following fundamental components: a central processing unit (CPU); a display device; at least one user input device; and memory for data storage.
There are two basic classifications of memory: volatile memory and non-volatile memory. The primary difference between volatile memory and non-volatile memory is that a volatile memory needs to be supplied with external power in order to hold and refresh data while a non-volatile memory can maintain data for extended periods of time without any power being supplied to the device. Consequently, data stored in volatile memory are typically lost when power to the host computer system is removed or cut-off, while data stored in non-volatile memory are typically retained when power to the host computer system is removed or cut-off.
Most computer systems utilize both volatile and non-volatile memory in the same system or device. For instance, in a typical computer system, data intended for high-speed short-term access, such as on-chip memory for the CPU, and often first and second level off-chip memory, are typically stored in volatile memory devices such as a cache or random access memory (RAM, DRAM, SRAM etc.) which typically have nanosecond to microsecond access times. However, in the same computer system, data intended for long-term storage or xe2x80x9cmass storagexe2x80x9d are typically stored in non-volatile storage devices such as magnetic disks, hard disk drives, zip drives, floppy disk drives, tape drives and optical storage media which typically have access times on the order of milliseconds or seconds.
As discussed above, volatile memory devices typically have significantly faster access times and higher data transfer rates than non-volatile storage devices. This, coupled with the decreasing cost of volatile memory over the past few years, makes volatile memory devices more desirable than non-volatile storage devices for use with high-speed systems. One reason non-volatile storage devices are so much slower than volatile memory devices is that non-volatile storage devices, such as disk drives, typically have moving parts and mechanical components such as rotating hard disks, rotating optical disks, rotating floppy disks, optical or magnetic readers, floating heads, lasers, tape drives and tape.
The mechanical components associated with non-volatile storage devices are problematic for several reasons. First, mechanical components slow down data transfer significantly because no mechanical mechanism is capable of achieving data transfer rates approaching the speed of a pure signal transfer between electronic components, i.e., electrical signals travel faster than any mechanical device can move. Second, mechanical components are subject to friction and motion stress and, therefore, even the best components physically wear out and degrade over time. This fact creates a long-term reliability problem and virtually guarantees that parts will need to be replaced in the field. In addition, to overcome friction and other mechanical forces, mechanical components typically require more power and therefore use up power resources faster. This is particularly disadvantageous in the present market that stresses compact size, including smaller battery packs and power supplies, as well as portability, lightweight and extended operation capability.
For the reasons discussed above, non-volatile storage devices are typically slower, less reliable and need more power to function than volatile memory devices. In contrast to non-volatile storage devices, volatile memory devices typically do not employ any moving parts or mechanical components. Therefore, volatile memory devices are faster, more reliable and need less power for operation than non-volatile storage devices. Consequently, volatile memory devices are potentially more desirable than non-volatile storage devices and represent an appealing alternative to non-volatile memory for computer systems requiring highly reliable data access at high-speeds with minimal power used.
As discussed above, volatile memory has numerous advantages in terms of speed, reliability and power consumption over non-volatile memory and non-volatile storage devices. However, the vast majority of long-term memory devices used in the prior art were non-volatile storage devices such as hard disk drives, zip drives and optical media. This industry-wide use of non-volatile memory for long term storage, despite the potential advantages of volatile memory, is primarily the result of the fact that using prior art volatile memory devices for long-term data storage involved unacceptable inherent risks, slow transfer rates between the host computer system and the memory and the addition of significant equipment resulting in significant additional cost.
FIG. 1 shows a typical prior art sub-system 100. Prior art sub-system 100 includes: motherboard 110; host computer system power supply 101; DC power connector 112, coupling motherboard 110 to power supply 101; AC power connector 157, coupling commercial AC power from outlet 199 to host computer system power supply 101; DC power connector 103, coupling power supply 101 to a non-volatile storage device 105 (typically a hard disk drive or optical storage device); disk controller 109; and a single data cable 107 that facilitates the exchange of data between non-volatile storage device 105 and disk controller 109.
In prior art sub-systems, such as sub-system 100 of FIG. 1, when power to sub-system 100 was shut down in a controlled and orderly manner no data were typically lost. However, when power was cut-off to the computer system, for any reason, the volatile memory lost all its data. Thus, using prior art volatile memory devices: if power was cut-off to the computer system in an unplanned manner, such as the user inadvertently unplugging the computer system or, in the case of a laptop or other portable system, allowing the battery to run down, all the data were lost; if power was interrupted by a local power failure such as a blown fuse or circuit breaker, all the data were lost; or if power was interrupted by a major power failure at a relay station or other power company source, all the data in volatile memory were lost. Consequently, using prior art volatile memory devices for long term data storage meant running the risk that even a temporary interruption of power would mean losing data forever.
In some prior art systems, a standard disk bus was used in an attempt to back up volatile memory to a dedicated disk drive. These prior devices addressed some of the problems discussed above. However, since these prior art devices employed dedicated disks and used standard disks buses, the devices were typically expensive to employ and had relatively slow data transfer rates between the host computer system and the memory device.
What is needed is a method that allows a host computer system to use volatile memory as the storage media, i.e., allows use of volatile memory as if it were a disk drive. The method should also provide the stability and security of non-volatile memory and, ideally, connect to an expansion bus of the host computer system, such as a PCI bus, to provide a sub-system that is faster than prior art systems at a relatively low cost.
According to the principles of the present invention, volatile memory devices are provided that are used by the host computer system as the storage media, i.e., they are used as if it were a disk drive. The volatile memory devices of the invention include an integrated controller and volatile memory storage media.
The volatile memory devices of the invention also include volatile memory device back up systems to provide power to both the volatile memory and non-volatile memory in the event of power failure. In one embodiment of the invention, the non-volatile memory that is backed up by the volatile memory device power supply of the invention is a local disk that is normally available to the host computer system. Consequently, the volatile memory devices of the present invention provide long-term data storage capability without the risks associated with prior art devices.
In addition, the volatile memory devices of the invention connect directly to an expansion bus of the host computer system, such as a PCI bus. Therefore, the volatile memory devices of the invention include a high-speed path to the host computer system. Consequently, the volatile memory devices of the invention are faster than prior art devices, use less power and are lower cost.
According to the principles of the invention, a computer system includes at least one volatile memory device and at least one non-volatile storage device. Under normal operating conditions, external commercial power is supplied to the volatile memory device to maintain the data, and to the non-volatile storage device, for normal operation by a host computer system power supply and commercial power source.
According to the principles of the invention, in the event of commercial power source loss, long-term data retention is maintained by using a volatile memory device power supply and rechargeable battery back up and control logic to maintain power to both the volatile memory device and the non-volatile storage device and transfer data from the volatile memory device to the non-volatile storage device through a back up and restore process.
In addition, according to the principles of the invention, the volatile memory device connects directly to a host computer system expansion bus so that a high-speed data path is provided for moving information between the host computer system and the volatile memory device.
In one embodiment of the invention, the volatile memory storage media of the volatile memory device of the invention is used for long-term data storage and is provided with continuous power, even when the host computer system loses power or is turned off. When the host computer system has power and is turned on, the data stored in the volatile memory device of the invention are normally immediately available and accessible with data transfer rates significantly faster than prior art volatile or non-volatile storage devices.
In one embodiment of the invention, data are then read from and written to the volatile memory device during the normal use of the host computer system as if the volatile memory device of the invention were a disk drive. Consequently, the volatile memory device of the invention is used in the same manner that non-volatile storage devices, such as a disk drive, were used in the prior art. However, since, according to the invention, the long-term storage is performed by a volatile memory device, the data transfer rates are faster, reliability is increased and less operating power is consumed.
In one embodiment of the invention, the user may manually initialize a back up procedure at any time. Once initiated, the back up procedure transfers the entire contents of the volatile memory to a non-volatile storage device. When this process is finished, the data in volatile memory are again available for normal use, and the back up data are unchanged. As discussed above, in one embodiment of the invention, the loss of commercial power to the host computer system will initiate an automatic back up from the volatile memory to the non-volatile storage device.
In one embodiment of the invention, upon the loss of commercial power, i.e., when the power at the outlet becomes unavailable, power will be provided seamlessly from a rechargeable battery system coupled to the both volatile memory and the non-volatile storage device. In addition, in one embodiment of the invention, an automatic back up from the volatile memory to the non-volatile storage device will be initiated, an alarm condition will be indicated, and the device will be shut down in an orderly manner.
In one embodiment of the invention, when commercial power is restored to the host computer system and the volatile memory device of the invention, the volatile memory device of the invention will then automatically restore the data previously saved on the non-volatile storage device to the volatile memory. The data are then available for normal access.
In particular, one embodiment of the invention includes a method for using volatile memory for data storage in a host computer system. The method includes: providing a volatile memory storage media; providing a non-volatile storage device; providing a volatile memory device power supply to supply power to both the volatile memory storage media and the non-volatile storage device in the event of power loss to the host computer system; providing control logic to transfer data from the volatile memory storage media to the non-volatile storage device in the event of power loss to the host computer system; and coupling the volatile memory to the host computer system using an expansion bus of the host computer system.
As discussed in more detail below, the volatile memory devices of the invention are used by the host computer system as the storage media and include volatile memory device back up systems to provide power to both the volatile memory and non-volatile memory in the event of power failure. In addition, the volatile memory devices of the invention connect directly to an expansion bus of the host computer system, such as a PCI bus. Consequently, the volatile memory devices of the invention are faster than prior art devices, use less power and are lower cost.
The volatile memory devices of the invention can be also readily used in existing standard computer system architectures that typically already include both volatile and non-volatile storage devices. In one embodiment of the invention, existing local disk dives are used as the non-volatile storage device that is backed up by the volatile memory device power supply of the invention. Therefore, the volatile memory devices of the invention will significantly increase the speed and data transfer rate of long-term data storage in virtually any host computer system.
It will be apparent in the discussion that follows that the volatile memory devices of the invention are a low cost solution to the long-standing problem presented by slow data transfer rates of prior art storage devices.
It is to be understood that both the foregoing general description and following detailed description are intended only to exemplify and explain the invention as claimed.